1. Field of the Invention
The present application relates generally to methods and compositions for depositing transition metal oxide thin films, such as titanium, zirconium and hafnium oxide thin films, by atomic layer deposition using metalorganic precursors. The metalorganic precursors comprise at least one cycloheptatriene (CHT) ligand.
2. Description of the Related Art
Atomic layer deposition (ALD) is a self-limiting process, whereby alternated pulses of reactants saturate a substrate surface. The deposition conditions and precursors are selected such that an adsorbed layer of precursor in one pulse leaves a surface termination that is non-reactive with the gas phase reactants of the same pulse. A subsequent pulse of different reactants reacts with the previous termination to enable continued deposition. Thus, each cycle of alternated pulses typically leaves no more than about one molecular layer of the desired material. The principles of ALD type processes have been presented by T. Suntola, e.g. in the Handbook of Crystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, Elsevier Science B. V. 1994, the disclosure of which is incorporated herein by reference. Variations of ALD have been proposed that allow for modulation of the growth rate. However, to provide for high conformality and thickness uniformity, these reactions are still more or less self-saturating.
While ALD processes can be used to deposit films at lower temperatures, typically CVD processes have been used for higher temperature growth because the reactions occur more rapidly at higher temperatures. In addition, some ALD processes can lose their self limiting nature at high temperatures. In some cases, higher temperatures can cause undesirable decomposition of some precursors. Some precursor decomposition can disrupt the self limiting nature of the ALD process, for example if the products of the decomposition reaction react with each other and/or react with the adsorbed species to deposit material on the substrate surface.
Atomic layer deposition (ALD) of Group IVB metal oxides, such as TiOx, ZrO2 and HfO2, has been studied for years. However, higher temperature ALD options for these metal oxides are quite limited. Metal halide reactants are typically used; however, metal halides are incompatible with some materials and processes. Some metal-organic precursors have also been used. However, these reactants have not been well suited for higher temperature deposition processes.